Dynamic quantitative risk assessment of LNG bunkering SIMOPs based on Bayesian network

Liquified natural gas(LNG)bunkering simultaneous operations(SIMOPs)refers to the operations(such as cargo operations,port activities and ship maintenance)occurring around LNG bunkering.SIMOPs pose new risks to LNG bunkering,because the operations are dynamically interlocked in which the occurrence probabilities of potential consequences change at different times due to commencement or completion of specific SIMOP events.However,traditional static risk assessment approaches are not able to take the dynamic nature of these new risks into account.This article proposes a dynamic quantitative risk as-sessment(DQRA)methodology based on the Bayesian network(BN)to develop better understanding of dynamic risks of LNG bunkering SIMOPs.The methodology is demonstrated and evaluated through a truck-to-ship LNG bunkering case study.The results and discussion of the case study validate the utility of the proposed methodology and demonstrate that BNs are efficient in performing the probability calcu-lations and are flexible in conducting causal diagnosis.The main innovation of this work is realizing the quantification of risks at different times,which reflects the most essential time-changing characteristics of risks associated with LNG bunkering SIMOPs.

Investigation of a ship resonance through numerical simulation

Understanding dynamic stability of a ship on a resonance frequency is important because comparatively smaller external forces and moments generate larger motions.The roll motion is most susceptible because of smaller restoring moments.Most studies related to the failure modes such as parametric roll and dead ship condition,identified by second generation of intact stability criteria(SGISC)are performed at a resonance frequency.However,the nature of resonance,where the model experiences an incremental roll motion,has not been well understood.In this study,nonlinear unsteady computational fluid dynamics(CFD)simulations were conducted to investigate the resonance phenomenon using a containership under a sinusoidal roll exciting moment.To capture the complexity of the phenomenon,simulations were conducted over a range of frequencies to cover the resonance frequency including lower and higher amplitudes.In addition to the resonance frequency,the phase shift between roll exciting moment and roll angle,as well as the phase difference between acceleration and roll angle,were found to have significant effects on the occurrence of resonance.